It is well known that many petroleum crudes, and heavy fractions thereof such as atmospheric or vacuum resids (the residue remaining after fractional distillation of crude oil to remove lighter components) contain coke precursors and metal compounds in amounts which adversely affect further down-stream processing and also, affect the quality of heavy fuels produced therefrom. Similarly, it is known that bitumens obtained from tar sands and heavy oil deposits are difficult and expensive to process because of their high content of asphaltenes and difficult to remove fine particles of inorganic solids.
The above-mentioned coke precursors include polycyclic hydrocarbons, asphaltenes and the like which tend to break down at elevated temperatures to form carbonaceous materials, often referred to as "coke." In subsequent processing coke may form on the interior walls of refining equipment or be deposited on catalyst to reduce its activity level. Hence, a feed-stock with a high coke forming tendency is undesirable. The coke forming tendency of an oil is generally evaluated by the Conradson Carbon method or the Ramsbottom Carbon method. A higher number from such an evaluation indicates a greater tendency for coke deposition on, for example, catalyst when the oil is processed by the fluid catalytic cracking (FCC) process wherein gas oils are cracked to produce gasoline and other lighter products. In the FCC process, coke is burned from the catalyst in a regenerator to restore catalyst activity and the regenerated catalyst is then recycled for the cracking of additional feed-stock.
The above-mentioned heavy oil charge-stocks often contain compounds of undesirable metals, including nickel and vanadium, which when deposited on FCC catalyst may adversely affect the physical properties of the catalyst and also promote the undesirable production of coke, hydrogren and other light hydrocarbon gases in the operation of the FCC process.
Similarly, the bitumen from tar sands contains minute, sometimes colloidal, particles of sand which, because of the difficulty of removal, cause processing problems in down-stream processing. Also heavy oil deposits often contain fine particles of solids, such as diatomite, which cause similar problems. Although there are vast deposits of such hydrocarbons, their development has been retarded because of the high cost of obtaining and processing synthetic crudes (syncrudes) from such deposits and problems caused by the high content of solids and asphaltenes.
The oil refining industry has long been plagued with the problem of maximizing high value transportation fuels (e.g., gasoline, jet, and diesel fuels) while minimizing the lower value fuel oil, especially residual oil, which is usually high in sulfur and metals. These heavy fuel oils, which are the heavy end of the crude oil, often require further upgrading to decrease the sulfur and metal contents.
The original oil refinery was a very simple batch distillation device in which crude oil was heated to separate the lighter more valuable products of naphtha and kerosene. It was discovered that further heating of the oil that was left after distillation of the lighter products of naphtha and kerosene from the crude oil would result in increased yield of lighter products. However, these additional products did not have the same characteristics as the naturally occuring (virgin) material in the crude oil and were considered "wild" and "unstable" and therefore undesirable. This discovery was what is now referred to as thermal cracking which was used for years as a method of decreasing the bottom of the barrel. As time progressed, the thermal cracking technology was relegated to the upgrading of the absolute bottom of the barrel or "vacuum bottoms." The virgin material in the crude which was heavier than kerosene or diesel but lighter than vacuum bottoms is now predominately upgraded by the fluid catalytic cracking process (FCC).
In order to produce the feed-stocks for the units in the refinery the simple batch distillation system was replaced with continuous distillation which consisted of a crude unit followed by a vacuum unit. Thus, this resulted in two distillation systems, both containing almost the same equipment of a charge heater, exchangers, and a distillation column. Both systems were required because the heavy atmospheric tower bottoms would thermally crack if a vacuum was not applied to the system to permit the separation to take place at a lower temperature. The refining industry is still trying to reduce the vacuum bottoms yield, but is limited by the equipment employed. This limit is imposed by the time-temperature relationship of the feed heaters. Normally one is limited to about 750 degrees F. on the outlet of the heater. Above this temperature thermal cracking will take place in the heater coils because of high temperatures and time. This thermal cracking results in coking of the heater tubes, overloading of the vacuum ejectors, and "unstable" products.
These processing limitations plus the decreasing availability of lighter crudes, are putting pressure on the industry to find acceptable methods to upgrade the vacuum bottoms. There are many technically feasible processes, but the economics are far from optimum. The hydrogen addition processes require high pressures and large volumes of catalyst, which result in high capital investments, high operating costs, and catalyst disposal problems. The carbon rejection processes are basically less capital intensive, but result in degraded products which need to be further treated, and therefore, increase the capital investment. These carbon rejection processes also produce undesirable byproducts such as high sulfur and high metals coke or, if they use a circulating solid, present a large catalyst disposal problem.
Many techniques are known for upgrading such hydrocarbon charge stocks contaminated with the above-described solids and solid-forming contaminants. For example, delayed and fluid coking processes are used. The coking process uses thermal conversion to produce coke and coker gasoline, coker gas oil, etc. The solid coke is usually high in ash and sulfur, and the distillate often must be further treated before it can be used for charging to catalytic cracking or blending. Solvent extraction and deasphalting processes also are used for preparing FCC charge-stocks from resids.
In U.S. Pat. No. 4,263,128, I have disclosed a process for upgrading whole crude and bottoms fractions from distillation of petroleum by high temperature, short time contact with a fluidizable solid of essentially catalytically inert character to deposit high boiling components of the charge stocks on the circulating solid, whereby Conradsen Carbon values, salt content and metal content are reduced. Therein, an inert solid, such as particles of kaolin clay, is supplied to a rising column of the charge in a contactor to vaporize most of the charge. Carbonaceous and metallic deposits formed on the particles of circulating solid are burned, after which the solid particles are recycled to the contactor.
In U.S. Pat. No. 4,435,272, I have disclosed a process for upgrading such charge-stocks by dispersing the charge introduced into a contactor into a descending curtain of heated particles of an added inert contact material. The charge is vaporized and carbonaceous materials, salt and metals are deposited on the circulating contact material. Deposits on the contact material are then burned off, the heat of combustion is absorbed by the contact material and the heated contact material is recycled to the contactor for vaporizing the charge.
It is also known to spray FCC feed into a riser reactor of a catalytic cracking unit to improve contact between the feed and catalyst.
Such known processes permit increased utilization of the crude (or syncrude) to produce transportation fuels, but they have high capital and operating costs and may create environmental concerns.
Therefore, a primary object of the present invention is to reduce the capital and operating costs of the typical refinery. It is a further object to minimize the environmental concerns while allowing the typical refiner to increase transportation fuels yield on crude and to eliminate or reduce the heavy fuel oil yield. These objects may be accomplished by using the process and apparatus of the present invention in place of the crude and vacuum units.
The present invention permits minimizing the degree of thermal cracking so that the products can be treated in existing downstream equipment. Further, the present invention makes it possible to eliminate the vacuum bottoms processing problems by removing over 95% of the metals and over 95% of the asphaltenes, and reducing the sulfur and nitrogen in the feedstock by 30 to 80% while at the same time removing any solids in the feedstock. This latter point is especially important in the upgrading of tar sands bitumens. Transportation fuel yields of 90% or more may be achieved, while the yield of heavy fuel oil may be reduced to 4% or less by use of the present invention. The virtual elimination of the catalyst poisons of metals and asphaltenes allows for the upgrading of the heavy oil product from this process in conventional downstream equipment such as fluid catalytic cracking, or gas oil hydrotreaters or hydrocrackers.
Additional objects and advantages of the present invention will be set forth in part in the following description and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out in the appended claims.